1. Field of the Invention
This invention relates generally to a tire manufacturing mold and a manufacturing method therefore, and more particularly to a tire manufacturing mold and a manufacturing method, based on discharge machining, in which a contour surface of the mold consisting of a predetermined curved surface corresponding to the outer circumferential surface of a tire being molded and bone portions and blade portions, both protruding on the contour surface, are integrally formed by discharge machining.
2. Description of the Prior Art
In manufacturing a tire manufacturing mold, plate-like protrusions (hereinafter referred to as blades) corresponding to grooves as commonly found of the tread surface of a tire must be formed on the tire mold. It is extremely difficult, however, to machine such blades on a tire metal mold with cutting operation, discharge machining, etc. in such a fashion that the blades are integrally formed with the mold proper. Heretofore, therefore, the following method has been commonly used. That is,
(i) Molds of the same size and shape as the segments obtained by radially dividing a tire being molded are prepared, using gypsum, for example, on the assumption that there exist no grooves on the tire
(ii) Metal pieces, for example, having the same cross-sectional shape as the grooves and a predetermined height are fitted, using adhesive and other appropriate means, on the gypsum models at positions corresponding to those of the grooves on the tire. Using these gypsum models as matrices, n pieces of their reversed molds are prepared with resin, etc.
(iii) Blades, made of stainless steel, etc., of a predetermined height are inserted into all the grooves formed on the reversed molds by the metal pieces. The predetermined height of the blade is such that the height of the blade excluding the portion being inserted into the groove is equal to the height of the blade being provided on the tire mold.
(iv) Gypsum is poured into the reversed molds with the blades and allowed to cure. Thus, gypsum casting molds are obtained by removing the reversed molds. At this time, the blades inserted in the reversed molds are moved to the casting molds with the portion thereof previously inserted in the reversed mold exposed on the casting mold.
(v) The gypsum casting molds thus formed are arranged in a ring shape and used as a matrix for molding the desired tire manufacturing mold with aluminum precision molding, for example.
With this method, the portion of the blade previously exposed on the casting mold is embedded in the tire manufacturing mold with the portion thereof previously embedded in the gypsum casting mold exposed on the tire manufacturing mold.
Another method of providing blades on a tire manufacturing mold is as follows.
Tire manufacturing metal molds without blade portions are first manufactured. And then, grooves corresponding to the cross-sectional shape of the blades are formed on the corresponding positions of the molds by manual metalworking or discharge machining, and prefabricated blades are embedded in these grooves.
These conventional methods, as described above, involve complex manufacturing processes, resulting in increased manufacturing costs. In addition, embedded blades are very likely to become loosened, coming off in some cases.